Abstract

For thirty years there have been numerous advances in the understanding of processes and concepts associated with the formation and alteration of petroleum accumulations. There has also been access to a geochemical data suite based on a large number of samples from piston cores, with some oil and gases, and lesser amounts of actual source rocks. Together these data have established the presence of a number of discrete source rock intervals within the Gulf of Mexico Basin ranging in age from Jurassic through the Eocene and their areal distribution. The lithology and depositional setting of these stratigraphic units has resulted in oils of different characters, including variable API (American Petroleum Institute) gravity values and sulfur contents. For the most part these different petroleum systems are geographically defined. Many of these oils have been altered, often reducing oil quality. There are, however, some processes, such as mixing and cracking, that may actually improve oil quality. Oil quality is of increasing economic importance as exploration shifts to deeper water and as reservoirs become more challenging as a result of the quality of the oil’s impact on producibility and price.